The main villain of Final Fantasy IX, Kuja is an androgynous/trap sorcerer who reveals himself to be a cruel manipulator and an more extreme narcissist, and he is responsible for the majority of the game's events.
Major spoilers
He is responsible for manipulating Brahne Raza Alexandros XVI to go to war; extracting Garnet til Alexandros XVII's eidolons and attempting to extract Eiko Carol's eidolons; creating the Black Mages to use as killer soldiers, and verbally tortures Vivi Ornitier about it; causing the events that led to Alexandria's destruction (and inadvertently making Garnet lose her voice); betraying Garland; destroying the planet Terra; and then threatening to destroy Gaia when he discovers he doesn't have long to live. As a Genome given a soul by Garland, Kuja can be considered the older brother of Zidane Tribal and Mikoto.